In an environmentally conscious and highly regulated society various industries have an ever increasing incentive to reduce undesired emissions. The coatings industry has addressed this challenge to some degree by developing systems which have low volatile organic content (VOC). completely solventless coatings which posses excellent physical properties being particularly prized. One type of solventless coating method gaining favor is powder coating. In brief, this method involves the application of a fine powder thermoplastic or thermoset resin formulation to a substrate using a technique such as dipping in a fluidized bed of the powder or electrostatic spraying therewith. After the substrate is coated, it is heated to fuse the powder into an adherent film. In the case of thermoset resins, the film may also be cured on the substrate.
As in the development of other coating systems, it has been found that powder coatings incorporating silicones, such as the compositions described in U.S. Pat. No. 3,170,890 to Boyd et al., can offer unique advantages over corresponding formulations based only on organic resin. However, known solid silicone resins based on phenyl and alkyl-functional siloxane units have limitations in that they generally exhibit poor flexibility and have limited compatibility with organic resins. Such silicone resins are generally prepared by hydrolyzing and condensing chlorosilanes or alkoxysilanes, the latter in the presence of an acid catalyst. Alternatively, it has been found that silicone resins can be synthesized from certain alkoxysilanes with the aid of a titanate catalyst. For example. U.S. Pat. No. 3,258,382 to Vincent teaches a method of hydrolyzing phenyl substituted or aliphatic hydrocarbon substituted alkoxysilanes using an orthotitanate or a partial condensate thereof.
Organosilicone compositions containing organotitanates are also known in the primer art. For example, United States Pat. No. 4,546,018 to Ryuzo et al. discloses primer compositions which promote adhesion of room temperature-curable silicone rubber to solid substrates. The primers comprise (A) a silicone-modified epoxy resin containing both epoxy and alkoxy groups and (B) an organotitanium acid ester.
U.S. Pat. No. 4.598,134 to Hirai et al. teaches a primer composition for heat-curable silicone rubber comprising (1) a component selected from (A) an organosilicon compound having at least one epoxy group and at least one silicon-bonded alkenyl group or silicon bonded hydrogen group or (B) a mixture of an organosilicon compound having silicon-bonded hydroxyl and silicon-bonded alkenyl or silicon-bonded hydrogen and an epoxy-functional alkoxysilane. (II) a trialkoxysilane containing a hydrogen or unsaturated aliphatic group and (III) and organotitanate ester.
U.S. Pat. No. 4,808,483 to Nakasuji et al. discloses primer compositions which are mixtures of (A) a reaction product of an alkoxysilane with an epoxy resin, (B) an epoxy-functional alkoxysilane and (C) a titanate. These primers are said to improve adhesion of room-temperature curable silicone rubber to various substrates.